Compensation - Activity Associated with Limited Partnership Units (Detail) (Limited Partnership Units [Member])	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Limited Partnership Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Units, Balance outstanding at beginning of period	31,207,729	68,480,097	45,814,354
Number of Units, Granted	42,416,871	50,908,986	41,691,703
Number of Units, Redeemed/exchanged units	(19,193,901)	(88,181,354)	(17,478,541)
Number of Units, Forfeited units	(868,709)		(1,547,419)
Number of Units, Balance outstanding at end of period	53,561,990	31,207,729	68,480,097

Number of exchangeable limited partnership units redeemed or exchanged into the Company's class A common stock during the period.

No definition available.

+ Details

Name:	bgcp_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentRedeemedExchanged
Namespace Prefix:	bgcp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares under non-option equity instrument agreements that were either cancelled or expired.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Net number of non-option equity instruments granted to participants.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant